The present invention relates to a vane pump which serves as a source of hydraulic fluid pressure mainly for a power steering system of a motor vehicle and, more particularly, to an improved cam ring for such a vane pump.
A vane pump of the type described is generally driven by an engine mounted on a motor vehicle to deliver a hydraulic fluid under pressure for operating a power cylinder, which is adapted to assist the operator of the motor vehicle in manipulating the steering wheel. Such a vane pump commonly includes a rotor carrying a plurality of vanes therewith, a cam ring receiving the rotor in its contoured bore, a pump shaft driving the rotor for rotation, a pump housing connected to one axial end of the rotor and cam ring, and a cover plate covering the other axial end of the rotor and cam ring and connected to the pump housing by suitable fastening means.
The cam ring must be highly resistive to wear and provide for good lubrication inasmuch as the radially outermost ends of the vanes slide in direct contact with the wall of the contoured bore in the course of rotation of the rotor. An implement heretofore proposed for meeting this requirement consists in sintering alloy powder which contains nickel (Ni), molybdenum (Mo), copper (Cu), or chromium (Cr), for example. The sintered alloy permits a working fluid to well infiltrate into its porous structure so that good lubrication and wear resistivity can be achieved. This enhances the performance and durability of the vane pump. Naturally, the exposed outer periphery of the cam ring is treated for preventing the working fluid from oozing out therefrom.
However, the use of such costly alloy powder for the cam ring contributes to an increase in the production cost of the whole vane pump.